Data-migration method

ABSTRACT

A method of migrating data from an old storage subsystem to a new storage subsystem in a data processing system which comprises host computers and storage subsystems. There is provided a route-changing phase before the data is migrated from the old storage subsystem to the new storage subsystem. In the route-changing phase, each host computer can access both the old and new storage subsystems and the new storage subsystem writes data into the old storage subsystem in response to a write request from the host computer and reads data from the old storage subsystem and sends the data to the host computer in response to a read request from the host computer.

BACKGROUND OF THE INVENTION

This invention relates to a method of migrating data from a storagesubsystem to another in a computer system. More specifically, thisinvention relates to a method of connecting a number of storagesubsystems and migrating data from old storage subsystems to new oneswithout affecting a plurality of host computers.

IBM proposed Extended Remote Copy (XRC) and Peer-to-Peer Remote Copy(PPRC) to migrate data which are stored in a storage system and which ahost computer is accessing (Implementing ESS Copy Services on S/390, IBMP. 502. 8. 5 DASD migration).

EMC proposed Symmetrix Data Migration Services (SDMS) (Symmetrix DataMigration Services, EMC Corporation,http://japan.emc.com/pdf/products/sdms/sdms_ds.pdf).

SUMMARY OF THE INVENTION

When data are to be migrated from an old storage subsystem to a newstorage subsystem in a data processing system according to the aboveprior art, all the host computers involved in the data migration have tobe stopped before the data are migrated. If the data processing systemis large and complex, data migration takes a long time, reducing theavailability of the system.

The object of the present invention is to provide a method of migratingdata in a data processing system without reducing the availability ofthe system even if the system is large and complex.

According to the present invention, there is provided a method ofmigrating data from an old storage subsystem to a new one in a dataprocessing system which comprises host computers and storage subsystems.There is provided a route-changing phase before the data-migrationphase. In the route-changing phase, each host computer can access boththe old and new storage subsystems and the new storage subsystem writesdata into the old storage subsystem in response to a write request froma host computer and reads data from the old storage subsystem and sendsthe data to the host computer in response to a read request from a hostcomputer.

According to the present invention, the availability of a dataprocessing system can be kept high if data migration takes place betweenstorage subsystems in the system.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be appreciated by the description whichfollows in conjunction with the following figures, wherein:

FIG. 1 is a schematic block diagram of an embodiment of data processingsystem according to the present invention;

FIG. 2 shows a configuration of a storage subsystem of the dataprocessing system of FIG. 1;

FIG. 3 is a flowchart of the data-migration processing of the dataprocessing system of FIG. 1.

FIG. 4 is an illustration of the workings of the data processing systemof FIG. 1;

FIG. 5 is a table of workings of old and new storage subsystems in eachphase of data-migration processing of the data processing system of FIG.1;

FIG. 6 is an example of a migration-control table of the data processingsystem of FIG. 1;

FIG. 7 is a flowchart of route-changing processing of the dataprocessing system of FIG. 1;

FIG. 8 is a flowchart of data-migration processing of the dataprocessing system of FIG. 1;

FIG. 9 is an illustration of data-writing processing in theroute-changing phase and the data-migration phase of the data processingsystem of FIG. 1;

FIG. 10 is a flowchart of the data-writing processing of FIG. 9;

FIG. 11 is an illustration of data-reading processing in theroute-changing phase and the data-migration phase of the data processingsystem of FIG. 1;

FIG. 12 is a flowchart of the data-reading processing of FIG. 11;

FIG. 13 is an illustration of access control by physical connection inthe data processing system of FIG. 1;

FIG. 14 is a block diagram of the data processing system of FIG. 1 whererestriction is imposed on access by zoning.

FIG. 15 is an illustration of access restriction of FIG. 14;

FIG. 16 is a block diagram of the data processing system of FIG. 1wherein access control is accomplished by the storage security function;

FIG. 17 is an illustration of the access control of FIG. 16;

FIG. 18 is a flowchart of data-migration processing with a debuggingmode of the data processing system of FIG. 1; and

FIG. 19 is an illustration of the data-migration processing of FIG. 18.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Referring to the drawing, embodiments of the present invention will bedescribed below.

FIG. 1 is a schematic block diagram of an embodiment of data processingsystem according to the present invention.

The data processing system comprises host computers 101 a and 101 b, anold storage subsystem 103 a, and a new storage subsystem 103 b. Thestorage subsystem 103 has a controller 201 to send and receive data toand from the host computers 101 a and 101 b and one or more disk storage210 to store data. Although the storage subsystems 103 a and 103 b ofthis embodiment are disk-array devices, they may be of other types.

The number of each of the host computer 101, the old storage subsystem103 a, and the new storage subsystem 103 b may be one or more.

Data are to be migrated from the old storage subsystem 103 a to the newstorage subsystem 103 b. The old and new storage subsystems 103 a and103 b are distinguished from each other by the reference letters “a” and“b”, but the reference letters will be omitted if it is unnecessary todistinguish between them.

The host computers 110 a and 101 b are work stations, microcomputers,mainframes, or the like wherein application programs are running ordatabase systems are operating.

Each storage subsystem 103 has one or more interfaces 104 and isconnected to the host computers 101 a and 101 b through a storage areanetwork (SAN) 102. The storage subsystems 103 may be connected directlywithout the SAN 102 to the host computers 101 a and 101 b. The interface104 is of a fibre channel, but it may be an interface for the storagesubsystem as a SCSI (Small Computer System Interface), iSCSI (internetSCSI), FICON, ESCON, or the like. No restriction is put on the structureof the SAN 102 or the kind of interfaces 104. As an example of theinterfaces 104, in the present embodiment, the fibre channel interfacewill be described.

Each storage subsystem 103 has one or more logical volumes 105. The hostcomputers 101 a and 101 b access the logical volumes 105 through theinterfaces 104 to read and write data from and in them. At this time,the protocol for storage subsystems provided by each interface 104 isused. FCP (Fibre Channel Protocol for SCSI) is used for fibre channelinterfaces. FC-SB (Single Byte Protocol) is used for FICON. Norestriction in particular is put on the kinds of protocols used in thedata processing system of the present invention.

The new storage subsystem 103 b has a data-migration program 106necessary for data migration, configuration information 107, controlinformation 108, update information 109, and data 110.

The data-migration program 106 executes data-migration processing. Theconfiguration information 107 and the control information 108 areinformation about the configuration and control of the storage subsystem103, and the data-migration program 106 refers to the information toexecute data-migration processing. Included in the control information108 is a progress pointer which indicates the progress of data-migrationprocessing and is used by the data-migration program 106.

The update information 109 is update information about write requestswhich the storage subsystem 103 b receives from host computers 101during data-migration processing. The update information 109 can be inthe format of a bit map or the like to be described later. The storagesubsystem 103 b is provided with a cache memory to store temporarilydata 110 about a read or write request from a host computer 101. Thecache memory raises the speed of ordinary data input/output processingand executes data processing at the time of data-migration processing(905 of FIG. 9 and 1105 of FIG. 11, etc.).

The data-migration program 106 uses a progress pointer and a bit map foreach logical volume 105 and executes data-migration processing fortheoretical volumes 105 one by one.

A data-migration program 106 is installed in a storage medium of eachstorage subsystem 103 from a device by using portable storage media suchas a compact disk or an optical magnetic disk, or through the medium ofa control network 111.

A migration-control host 112 is provided, which is a workstation,personal computer, mainframe, or the like and has a CPU, a memory, and astorage. A migration-control program 113 runs in the CPU to control themigration of data from the old storage subsystem 103 a to the new one103 b. A migration-control table 114 is held in the memory (or thestorage).

The migration-control program 113 uses the migration-control table 114to monitor and control data-migration processing. To be concrete, themigration-control program 113 monitors the conditions of storagesubsystems 103, which are connected to the migration-control host 112through the control network 111, and implements the change ofconfiguration, data-migration processing, etc. A control network 111 isgenerally configured of Ethernet (registered trademark) using theInternet Protocol, but it may be of any type.

The migration-control program 113 sends the whole or a part of themigration-control table 114 to the data-migration program 106 of the newstorage subsystem 103 b. Based on the whole or the part of themigration-control table 114 thus sent from the migration control program113, the data-migration program 106 prepares the configurationinformation 107 and the control information 108.

Although the migration-control host 112 is provided separately from thehost computers 101 and the storage subsystems 102, the migration-controlprogram 113 and the migration-control table 114 may be installed in anydevice in the system execute data-migration processing.

FIG. 2 shows the configuration of a storage subsystem 103.

The storage subsystem 104 has a controller 201 and one or more diskstorages 210. The controller 201 has a host adapter 203, a memory 205,one or more disk adapters 207, a processor (CPU) 202, and a networkcontroller 204. Although the number of each component is irrelevant tothe substance of the present invention, multiplexing is preferable fromthe viewpoint of performance and reliability. The host adapter 203controls the protocol for the interfaces 104 such as fibre channels.

The network controller 204 controls the protocol for the control network111 and implements communication with the migration-control host 112.

Stored in the memory 205 are a program and data for data-migrationprocessing. To put it concretely, stored in the memory 205 are thedata-migration program 106, configuration information 107, controlinformation 108, update information 109, and data 110 to accomplish datamigration. Also stored in the memory 205 are a control program andcontrol information for the control of storage subsystems 103 and cachedata 110 for input and output processing to and from the host computers101. It is preferable to provide mirrored memories 205 and dualpowersupplies for the memories 205 to raise reliability.

In the same way as the host adapter 203, the disk adapters 207 processthe protocol for a disk interface or interfaces 209 such as fibrechannels or the like.

The disk storage or storages 210 receive commands to read and write fromthe controller 201 through the disk interface or interfaces 209 andimplement the processing prescribed by the commands. It is preferable toprovide each disk storage 210 with dual disk interfaces 209 to raisereliability.

Each storage subsystem 103 has a redundant structure wherein two or moredisk storages 210 are combined and logical devices (logical volumes) 105are formed. The processor (CPU) 202 executes the processing for thestorage subsystems 103. The processor 202 is connected through aninternal bus 208 to the host adapter 203, disk adapters 207, and networkcontroller 204 inside the controller 201, and the processor 202 controlsthe host and disk adapters 203 and 207 and the network controller 204.The processor 202 is also connected to the memory 205 through theinternal bus 208, loads the data-migration program 106 and the controlinformation 108 stored in the memory 205 into itself, and implements thedata-migration program 106. The old storage subsystem 103 a has theconfiguration of FIG. 2, in the same way as the new storage subsystem103 b. However, the old storage subsystem 103 a will do if it hasfunctions to send and receive data to and from the host computers 101.

Although the storage subsystem 103 of the present embodiment has beendescribed by adopting a simple internal structure, no restriction is puton the internal structure so long as the storage subsystem 103 has equalfunctions. For example, switches may be use instead of the internal bus208 to accomplish communication among components of the controller 201as disclosed in Japanese Unexamined Patent Publication No. 10-333836.

FIG. 3 is a flowchart of the data-migration processing of the dataprocessing system of the present embodiment. FIG. 4 is an illustrationof the workings of the data processing system of the present embodiment.

In FIG. 4, data-migration processing is executed by the data-migrationprogram 106 of the new storage subsystem 103 b, and the data stored inthe old storage subsystem 103 a are migrated to the new storagesubsystem 103 b.

First of all, the migration-control program 113 initializes the system(FIG. 4 a) for data migration. To put it concretely, themigration-control program 113 pairs a logical volume 105 a of the oldstorage subsystem 103 a and a logical volume 105 b of the new storagesubsystem 103 b. At this time, relevant host computers 101 (informationabout application programs, file systems, etc. which run in the relevanthost computers 101) are set up, too (301. FIG. 4 a).

After the initialization, the new storage subsystem 103 b is connectedto the SAN 102; i.e., the new storage subsystem 103 b is added to thedata processing system (302. FIG. 4 b). At this time, though the newstorage subsystem 103 b is physically connected to the SAN 102, themigration-control program 113 gives the new storage subsystem 103 b aninstruction to refuse access from the host computers 101.

Then, route-changing processing is started (303) to shift the routes ofthe host computers 101 from the old storage subsystem 103 a to the newone 103 b. The migration-control program 113 instructs every new storagesubsystem 103 b under the control of the migration-control table 114 tooperate as follows.

While the route-changing processing is being done, the route-changedhost computer 101 a accesses the new storage subsystem 103 b. When thenew storage subsystem 103 b receives a read request from the hostcomputer 101 a, it reads the requested data from the old storagesubsystem 103 a and sends them to the host computer 101 a. When the newstorage subsystem 103 b receives a write request from the host computer101 a, it writes the data to be updated in the old storage subsystem 103a (FIG. 4 c).

On the other hand, the route-unchanged host computer 101 b accesses theold storage subsystem 103 a (FIG. 4 c). The route change of hostcomputers 101 is to change the subject of access by the host computers101 from the old storage subsystem 103 a to the new one 103 b. Forexample, if the protocol is of a fibre channel, access information(World Wide Name or WWN) held in the host computers 101 is changed frominformation about the old storage subsystem 103 a to information aboutthe new one 103 b. If the protocol is of iSCSI, the iSCSI name ischanged from the old storage subsystem 103 a to the new storagesubsystem 103 b. The operator of the system may change the configurationfiles manually for the route-changing processing. The route-changingprocessing can also be accomplished by making a route-control program(for example, Hitachi Dynamic Link Manager, or HDLM, or the like) ineach host computer 101 and the migration-control program 113 work incooperation with each other.

After the route-changing processing of all the host computers 101, theydo not access the old storage subsystem 103 a, but the new one 103 b(FIG. 4 d).

After the route-changing processing, data-migration processing isexecuted (304). The migration-control program 113 gives the new storagesubsystem 103 b instructions to migration the data in the old storagesubsystem 103 a to the new one 103 b itself.

After the data-migration processing, the old storage subsystem 103 a isdisconnected from the SAN 102. Thus, the old storage subsystem 103 a iseliminated from the data processing system (FIG. 4 f). Accordingly, thedata in the old storage subsystem 103 a can be erased and the oldstorage subsystem 103 a can be formatted and then loaded into anothersystem to be used for other purposes.

During the above processing, the old and new storage subsystems 103 aand 103 b work differently from each other in each step in theprocessing. The migration-control program 113 controls the steps of theprocessing and gives the old and new storage subsystems 103 a and 103 binstructions about their workings.

FIG. 5 is a table of workings of old and new storage subsystems 103 aand 103 b in each phase of data-migration processing.

As shown in FIG. 5, there are four phases; i.e., a phase before routechange 505, a route-changing phase 506, a data-migration phase 507, anda phase after data migration 508. The steps 301 and 302 of the flowchartof FIG. 3 correspond to the phase before route change 505; the step 303,to the route-changing phase 506; the step 304, to the data-migrationphase 507; the step after the step 304, to the phase after datamigration 508.

The column 501 of the table of FIG. 5 shows the numbers of phases; thecolumn 502, reading and writing of the old storage subsystem 103 a; thecolumn 504, reading and writing of the new storage subsystem 103 b.

The old storage subsystem 103 a makes ordinary workings beforedata-migration processing (in the phase before route change 505 and theroute-changing phase 506); i.e., the host computers 101 read and writedata from and into the old storage subsystem 103 a. After data-migrationprocessing (in the data-migration phase 507 and the phase after datamigration 508), the old storage subsystem 103 a is made inaccessiblefrom the host computers 101.

The new storage subsystem 103 b is inaccessible from the host computers101 in the phase before route change 505.

If the new storage subsystem 103 b receives a write request after theroute-changing phase 506 but before data-migration phase 507, itreceives the data to be written and then write the data in the oldstorage subsystem 103 a. If the new storage subsystem 103 b receives aread request after the route-changing phase 506 but beforedata-migration phase 507, it reads data from the old storage subsystem103 a because the latest data are stored in it and then sends therequested data to the host computer 101. In other words, the new storagesubsystem 103 b works in response to read and write requests from thehost computers 101 so that the old storage subsystem 103 a will beupdated.

In the data-migration phase 507, the new storage subsystem 103 bmigrates the data in the old storage subsystem 103 a to itself.Accordingly, the data are read out of the old storage subsystem 103 a inresponse to a request for reading data not yet migrated to the newstorage subsystem 103 b. The data are read out of the new storagesubsystem 103 b in response to a request for reading data alreadymigrated to the new storage subsystem 103 b. The data are written intothe new storage subsystem 103 b in response to write requests.

Because the latest data are stored in the new storage subsystem 103 b inthe phase after data migration 508, the host computers 101 instructs thenew storage subsystem 103 b to read and write data from and into the newstorage subsystem 103 b itself in the phase after data migration 508.

FIG. 6 is an illustration of the migration-control table 114.

The migration-control table 114 is prepared by the migration-controlprogram 113 and stored in the migration-control host 112. Themigration-control program 113 controls and implements data migration inaccordance with the migration-control table 114. A unit for controlcalled “migration group” is laid down for data-migration processing. Thelogical volume 105 are the minimum unit, and the optimum unit such ashost computer 101, file system, application program, user, department,floor, building, or the like is adopted as the unit for control.

Each migration group is allotted a specific group ID, or identifier,601. The migration-control program 113 controls the migration of eachmigration group by using the column of migration status 602. Eachmigration group controls the old storage subsystem 103 a and the newstorage subsystem 103 b by using the old storage subsystem's ID 603 andthe new storage subsystem's ID 604, respectively, for each volume to bemigrated. The storage subsystems 103 and the logical volumes 105 in thestorage subsystems 103 which each migration group belongs to can beidentified based on the new storage subsystem 103 b by using the oldstorage subsystem's ID 603 and the new storage subsystem's ID 604.

Further included in the migration-control table 114 is a detailedinformation column 605 which holds, for example, information aboutdirectory of each migration group. A controller of data-migrationprocessing can easily recognize the contents of migration groups fromthe detailed information 605 and determine the schedule, procedure, etc.of the whole data-migration processing.

The migration-control program 113 designates the progress ofdata-migration processing by logical volumes based on themigration-control table 114. Besides, the migration-control program 113designates phases (defined in FIG. 5) to the old and new storagesubsystems 103 a and 103 b.

[Route-Changing Processing]

FIG. 7 is a flowchart of route-changing processing (step 303 of FIG. 3).

The route-changing processing is made for each migration group. FIG. 7shows the details of route-changing processing of a migration group.There is a pair or pairs of logical volumes 106 to be migrated for eachmigration group.

First of all, the migration-control program 113 ascertains whether thereare route-unchanged host computers 101 or not among those belonging tothe migration group to be migrated (701).

When the routes of all the host computers 101 have been changed,route-changing processing is ended and data-migration processing (step304 of FIG. 3) is executed. The access from host computers 101 to thelogical volumes 105 a of the old storage subsystem 103 a in themigration group is restricted. Restriction of access can be made byseveral methods, of which the details will be described later. At thistime, a communication line between the old and new storage subsystems103 a and 103 b is secured (702). Then, the migration group is advancedfrom the “route-changing phase” to the “data-migration phase” on themigration-control table 114.

If there are route-unchanged host computers 101, their routes arechanged (706–708).

First, chosen among the route-unchanged host computers 101 is one whoseroute is to be changed next (703).

Then, it is ascertained whether there are route-unchanged storagesubsystems 103 (704). Next, chosen regarding the chosen route-unchangedhost computer 101 is a route-unchanged storage subsystem 103 which is toundergo route-changing processing (705). At this time, all the logicalvolumes 105 of the storage subsystem 103 relating to the host computer101 undergo the following route-changing processing (706–708). The hostcomputer 101 disconnects itself from the storage subsystem 103 relatingto the route-changing (706). This disconnection can usually beaccomplished by an unmounting function provided by the operating systemof the host computer 101 or by a route control program such as HDLM orthe like described earlier.

Because the new storage subsystem 103 b has an identifier different fromthat of the old storage subsystem 103 a, the host computer 101 changesset information about the storage subsystem 103 to change the route(707). If the interface is of a fibre channel or SCSI (FCP), the WWN isused as the identifier of the storage subsystem 103. If the interface isof iSCSI, the iSCSI name is used as the identifier of the storagesubsystem 103. If the interface is of FICON, the WWN or port ID of thefibre channel is used as the identifier of the storage subsystem 103.

A storage subsystem 103 may have one or more identifiers, and a hostcomputer 101 may have a plurality of identifiers against one storagesubsystem 103. In this case, route-changing processing is made for onlyidentifiers relating to the route-changing processing specified in themigration-control table 114.

After finishing the route change, the host computer 101 connects itselfto the storage subsystem 103 relating to the route change (708). Thisconnection can usually be accomplished by amounting function provided bythe operating system of the host computer 101.

Thereafter, the processing of steps 704 to 708 is repeatedly executeduntil the route-changing processing of all the storage subsystems 103 iscompleted. When the route-changing processing of all the storagesubsystems 103 is completed, it is again ascertained whether there areroute-unchanged host computers 101 or not. Then, the processing of steps703 to 708 is repeatedly executed until the route-changing processing ofall the host computers 101 in the migration group is completed.

Although storage subsystems 103 are changed one by one in theroute-changing processing described above, the route-changing processingof a plurality of storage subsystems 103 may be made at a time(704–708).

In addition, although one host computer 101 is chosen based on themigration-control table 114 and then the route-changing processing forstorage subsystems 103 relating to the chosen host computer 101 is madein the route-changing processing described above, one storage subsystem103 may first be chosen and then the route-changing processing for hostcomputers 101 relating to the chosen storage subsystem 103 may be made.

[Data-Migration Processing]

FIG. 8 is a flowchart of details of data-migration processing (step 304of FIG. 3).

Data-migration processing is executed by the data-migration program 106of each new storage subsystem 103 b. FIG. 8 shows the processing of eachlogical volume 105.

First of all, various variables for data-migration processing areinitialized (801). Control information 108 such as a progress pointerindicating progress of migration and the phases of migration and updateinformation 109 such as a bit map showing the state of updating areinitialized as representative variables. A bit map is used to controlmigration areas in the data-migration processing described below.

The data-migration program 106 allots a one-bit flag to every unit forcontrol and forms a bit map showing migration and non-migration. Thesize of the unit for control may be one block (512 bytes) often used bySCSI, etc. or any size (for example, one megabyte). If the bit of a unitfor control is on (the value of the bit is “1”), the unit is in thelatest state and data migration is unnecessary. If the bit of a unit forcontrol is off (the value of the bit is “0”), the unit is not in thelatest state and data migration is necessary. The data-migration program106 set all the bits zero at the time of initialization and then startsdata-migration processing.

The column 502 (“Status of Migration”) of FIG. 5 shows the four phasesof data-migration processing; i.e., a phase before route change 505, aroute-changing phase 506, a data-migration phase 507, and a phase afterdata migration 508. The progress pointer indicates the progress of datamigration and is initialized to indicate the head of the logical volume105. Every time data are migrated, the data-migration program 106updates the progress pointer. Usually the progress pointer indicates anaddress of the logical volume 105. For example, the value of theindicated address is increased by adding the number of bytes of migrateddata to the progress pointer.

The data-migration program 106 of the new storage subsystem 103 b refersto the progress pointer of the logical volume 105 under data migrationto ascertain the progress of data migration (802). When the progresspointer indicates the end of the logical volume 105, the data migrationof the logical volume 105 is complete.

The data-migration program 106 checks the condition of the areaindicated by the progress pointer in order to migration the data in thearea (803). If the indicated area is not used to read or write data, thedata-migration program 106 locks the area (805) and advances to the nextprocessing. If the indicated area is used to read or write data, thedata-migration program 106 waits for the area to become usable (804),locks the area (805), and advances to the next processing.

The data-migration program 106 reads data from the indicated area of theold storage subsystem 103 a (806), store the data in a cache memory 110,and writes the data in a disk storage 210 of the new storage subsystem103 b (807).

The data-migration program 106 updates the control information about thedata migrated from the old storage subsystem 103 a to the new one 103 b.The data-migration program 106 turns on the bit corresponding to thearea of migrated data (808) and moves the progress pointer forward bythe size of the area (809).

Because mirrored cache memories 110 are usually provided and they arenonvolatile, data migrated from the old storage subsystem 103 a to thenew one 103 b do not necessarily need to be written in the disk storage210 as timely as described above. The data-migration program 106 mayupdates the progress pointer and the bit map immediately after storingmigrated data in the cache memory 110 and advance to the nextdata-migration processing.

[Write Processing]

FIG. 9 is an illustration of data-writing processing in theroute-changing phase and the data-migration phase. FIG. 10 is aflowchart of the processing.

In the route-changing phase (FIG. 9 a), data 901 to be written into thenew storage subsystem 103 b by the host computer 101 are not writteninto the disk storage 210 of the new storage subsystem 103 b, but thedisk storage 210 of the old storage subsystem 103 a. In other words, nodata are written into the disk storage 210 of the new storage subsystem103 b and all data are written into the disk storage 210 of the oldstorage subsystem 103 a in the route-changing phase.

To put it concretely, the new storage subsystem 103 b receives data 901from a host computer 101, stores the data 901 in its cache memory 110,and writes the data 901 into the disk storage 210 of the old storagesubsystem 103 a. Then, after writing the data 901 into the disk storage210 of the old storage subsystem 103 a, the new storage subsystem 103 breturns the result 904 of the writing processing to the host computer101. Because data-migration processing is not made in the route-changingphase, the bit map 109 is not updated (903).

In the data-migration phase (FIG. 9 b), data 901 to be written into thedisk storage 210 of the new storage subsystem 103 b by a host computer101 are written into the disk storage 210 of the new storage subsystem103 b.

To put it concretely, the new storage subsystem 103 b receives data 901from a host computer 101 and stores the data 901 in its cache memory110. If data in the area which is the subject of writing have not yetbeen migrated, the new storage subsystem 103 b migrates the data of thearea.

The control unit for data migration is different from the access unit ofthe host computers 101 (the former is usually larger than the latter).If the area which is the subject of the writing of data 901 is smallerthan the control unit for data migration, the new storage subsystem 103b reads data, whose size is equal to the control unit, relating to thearea from the old storage subsystem 103 a (905) and writes the data inthe cache memory 110.

Then, the data read out of the old storage subsystem 103 a and the data901 received from the host computer 101 are merged together in the cachememory 110 and written into the disk storage 210 of the new storagesubsystem 103 b. At the same time, the corresponding bit of the bit map109 controlling the data migration is turned on (906).

Referring to FIG. 10, the data-writing processing will be detailed.

When the data-migration program 106 of the new storage subsystem 103 breceives a write request from a host computer 101, it checks thecondition of data-migration processing (1001). Because the new storagesubsystem 103 b is inaccessible in the phase before route change 505(see FIG. 5), an error status is returned to the host computer 101 if anaccess request is received from a host computer 101 in the phase beforeroute change 505 (1002). Because the new storage subsystem 103 b isaccessible in the other phases, the processing is continued if an accessrequest is received.

The data-migration program 106 of the new storage subsystem 103 banalyzes the contents of the write request (1003), chooses an areacorresponding to the address specified by the write requests, and locksa data-storing area in the cache memory 110 (1004). At this time, if thesize of the data relating to the write request is larger than theavailable storage area of the cache memory 110, the processing of steps1004 to 1014 is repeated until all the data are received (1015).

The data-migration program 106 receives the data to be written from thehost computer 101 and stores the data in the area locked in the cachememory 110 (1005).

Then, the data-migration program 106 checks to see if the system is inthe route-changing phase (1006) and writes the data into the old storagesubsystem 103 a if the system is in the route-changing phase (1007).When the writing of all the data is completed (1015), the data-migrationprogram 106 returns the result of the processing to the host computer101 and the writing processing comes to an end.

If the system is not in the route-changing phase 506, the data-migrationprogram 106 checks to see if the system is in the data-migration phase507 (1008). If the system is in the data-migration phase 507, thedata-migration program 106 refers to the progress pointer and the bitmap to find whether data migration has already taken place in the arearelating to the writing or not (1009).

If data migration has already taken place in the area, thedata-migration program 106 writes the data into the new storagesubsystem 103 b (1014). Namely, the same writing processing is made inthe new storage subsystem 103 b as in an ordinary storage subsystem.Because data migration has taken place in the whole area when datamigration has been completed, data are thereafter written into the newstorage subsystem 103 b.

If migration has not yet taken place in the area relating to thewriting, the data-migration program 106 reads data out of the oldstorage subsystem 103 a (1010), merges the data read from the oldstorage subsystem 103 a and the data 901 received from the host computer101 together in the cache memory 110 to form data for a new area (1011).To put it concretely, the data in the corresponding area in the dataread out of the old storage subsystem 103 a are replaced by the data901.

Then, the data-migration program 106 writes the formed data for a newarea into the disk storage 210 of the new storage subsystem 103 b (1012)and turns on the bit of the new area to indicate that data migrationtook place in the new area (1013).

After all the data relating to the write request undergo the aboveprocessing, the data-migration program 106 returns the result of thewrite request to the host computer 101 (1016).

The data writing (1007, 1012, and 1014) has to be made before the step1016 to ensure the consistency of data. However, the data writing in thesteps 1012 and 1014 may be made out of synchronism with the step 1016because data are written into the new storage subsystem 103 b and thecache memory 110 of the new storage subsystem 103 b ensures theconsistency of data.

Described above is a data migration method of reading data from the oldstorage subsystem 103 a, merging the data thus read and the data 901received from a host computer 101 together, and writing the added datainto a disk storage 210 of the new storage subsystem 103 b; however,data migration can be controlled by using the progress pointer alone,without using the bit map. In this case, although data to be written 901are all written into a disk storage 210 of the new storage subsystem 103b, data 901 to be written into an area, where data migration has not yettaken place, with an address larger than the progress pointer arewritten into the old storage subsystem 103 a too. Thereafter, the dataare migrated from the old storage subsystem 103 a to the new one 103 bby the data-migration processing of FIG. 8.

[Read Processing]

FIG. 11 is an illustration of data-reading processing in theroute-changing phase and the data-migration phase. FIG. 12 is aflowchart of the processing.

Because the latest data from the host computers 101 are not stored inthe new storage subsystem 103 b in the route-changing phase (FIG. 11 a),data 1201 are read out of the old storage subsystem 103 a (1102).

To put it concretely, the new storage subsystem 103 b reads the data1101, which a host computer 101 required, from a disk storage 210 of theold storage subsystem 103 a and stores the data 1101 in its cache memory110. The new storage subsystem 103 b sends the data 1101 to the hostcomputer 101. After finishing the transmission of the data 1101, the newstorage subsystem 103 b sends the status 1104 to the host computer 101.In the route-changing phase, data-reading processing does not entaildata migration and hence the bit map 109 is not updated.

If the data 1101 required by a host computer 101 have not yet beenmigrated in the data-migration phase (FIG. 11 b), the data of the areawhere reading has taken place are migrated.

To put it concretely, the control unit for data migration is differentfrom the access unit of the host computers 101 (the former is usuallylarger than the latter). If the area which is the subject of the readingof the required data 1101 is smaller than the control unit for datamigration, the new storage subsystem 103 b reads data, whose size isequal to the control unit, relating to the area from the old storagesubsystem 103 a (1105) and stores the read-out data in the cache memory110.

Then, the new storage subsystem 103 b sends the required data 1101 tothe host computer 101. Thereafter, the new storage subsystem 103 bmigrates the read-out data stored in the cache memory 110 to its diskstorage 210 and turns on the corresponding bit of the bit map 109(1103).

Referring to FIG. 12, data-reading processing will be detailed below.

The data-migration program 106 of the new storage subsystem 103 b checksthe condition of data-migration processing when it receives a requestfrom a host computer 101 (1201). Because the new storage subsystem 103 bis inaccessible in the phase before route change 505 (see FIG. 5), anerror status is returned to the host computer 101 if an access requestis received from a host computer 101 in the phase before route change505 (1202). Because the new storage subsystem 103 b is accessible in theother phases, the processing is continued if an access request isreceived.

The data-migration program 106 of the new storage subsystem 103 banalyzes the contents of the read request (1203), chooses an areacorresponding to the address indicated by the write request, and locks adata-storing area in the cache memory 110 (1204). At this time, if thesize of the data relating to the read request is larger than theavailable storage area of the cache memory 110, the processing of steps1204 to 1213 is repeated until all the data are sent (1214).

The data-migration program 106 checks to see if the system is in theroute-changing phase (1205) and read data from the old storage subsystem103 a if the system is in the route-changing phase (1206). When thereading of all the data is completed (1215), the data-migration program106 returns the status to the host computer 101 (1215) and the readingprocessing comes to an end.

If the system is not in the route-changing phase 506, the data-migrationprogram 106 checks to see if the system is in the data-migration phase507 (1207). If the system is in the data-migration phase 507, thedata-migration program 106 refers to the progress pointer and the bitmap to find whether data migration has already taken place in the arearelating to the reading or not (1208).

If data migration has already taken place in the area, thedata-migration program 106 reads data from the new storage subsystem 103b (1014). Namely, the same reading processing is made in the new storagesubsystem 103 b as in an ordinary storage subsystem. Because datamigration has taken place in the whole area when data migration has beencompleted, data are thereafter read from the new storage subsystem 103b.

If migration has not yet taken place in the area relating to thereading, the data-migration program 106 reads data out of the oldstorage subsystem 103 a (1209), stores the data (hereinafter “new-areadata”) in the cache memory 110. Then, data-migration program 106 writesthe new-area data into a disk storage 210 of the new storage subsystem103 b (1210) and turns on the bit corresponding to the new area toindicate that data migration took place in the new area (1211).

The new storage subsystem 103 b sends the data 1101 required by the hostcomputer 101 of the new-area data to the host computer 101 (1213).

After processing all the data relating to the read request as describedabove, the data-migration program 106 sends the status to the hostcomputer 101 (1215).

The writing of data (1210) during the above data-reading processing hasto be made before the step 1215 to ensure the consistency of data.However, the writing may be made out of synchronism with the step 1215because the cache memory 110 of the new storage subsystem 103 b ensuresthe consistency of data.

Described above is a method of migrating the data upon a request forreading data which are not yet migrated and writing the data into a diskstorage 210 of the new storage subsystem 103 b; however, data migrationcan be controlled by using the progress pointer alone, without using thebit map. In this case, upon a request for reading data 1101 which arenot yet migrated, the new storage subsystem 103 b reads only the data1101 from the old storage subsystem 103 a and sends them to the hostcomputer 101 without migrating them to itself. Thereafter, the data aremigrated from the old storage subsystem 103 a to the new one 103 b bythe data-migration processing shown in FIG. 8.

[Restriction of Access]

FIGS. 13 to 17 shows examples of restriction of access to the storagesubsystems 103. A method of controlling access by physical connectionand a method of controlling access logically are conceivable. Besides,in the case of logical restriction, access may be restricted on the sideof the network or on the side of the storage subsystems 103. Embodimentsof these three methods will be described below.

[Example by Wire Connection]

FIG. 13 is an illustration of access control by physical connection.

There are a SAN 102 a for the old storage subsystem 103 a and a SAN 102b for the new storage subsystem 103 b. As shown in FIG. 5, there arefour phases in data-migration processing; i.e., a phase before routechange 505, a route-changing phase 506, a data-migration phase 507, anda phase after data migration 508, which correspond to FIGS. 13 a, b, c,and d, respectively.

In the phase before route change 505, the new storage subsystem 103 b isnot connected to the SAN 102 a which is connected to the old storagesubsystem 103 a. Thus, the old and new storage subsystems 103 a and 103b are physically disconnected. Besides, because the host computer 101 isnot connected to the SAN 102 b of the new storage subsystem 103 b, thehost computer 101 cannot access the new storage subsystem 103 b (FIG. 13a).

In the route-changing phase 506, the new storage subsystem 103 b isconnected to the SAN 102 a of the old storage subsystem 103 a and thehost computer 101 can access the new storage subsystem 103 b. Thus, theroute change of the host computer 101 is possible. Besides, because theold storage subsystem 103 a is connected through the SAN 102 a to thenew storage subsystem 103 b, the new storage subsystem 103 b can accessthe old storage subsystem 103 a for route-changing processing (FIG. 13b).

Upon the completion of route change of the host computer 101, the systemadvances into the data-migration phase 507, wherein access from the hostcomputer 101 to the old storage subsystem 103 a has to be prohibited.Accordingly, in the data-migration phase 507, the host computer 101 isconnected to the SAN 102 b so that the host computer 101 can access thenew storage subsystem 103 b through the SAN 102 b. Besides, the old andnew storage subsystems 103 a and 103 b are left connected to the SAN 102a in order to migrate data (FIG. 13 c).

In the phase after data migration 508, it is no more necessary for thenew storage subsystem 103 b to access the old storage subsystem 103 a;accordingly, the old storage subsystem 103 a and the SAN 102 a aredisconnected from the new storage subsystem 103 b. Because the hostcomputer 101 is connected to the SAN 102 b, the host computer 101 canaccess the new storage subsystem 103 b through the SAN 102 b (FIG. 13d).

The host computer 101 may access the new storage subsystem 103 bdirectly and through no SAN 102. In this case, three lines are necessaryin the route-changing phase 506; i.e., one connecting the host computer101 and the old storage subsystem 103 a, one connecting the hostcomputer 101 and the new storage subsystem 103 b, and one connecting theold and new storage subsystem 103 a and 103 b. Necessary in thedata-migration phase 507 are dual lines, one connecting the old storagesubsystem 103 a to the new one 103 b and the other connecting the hostcomputer 101 to the new storage subsystem 103 b.

If no SAN 102 is used, the connectibility of the new storage subsystem103 b is reduced; therefore, it is preferable to use SANs 102 when alarge-scale data processing system with many host computers 101 andstorage subsystems 103 is to be configured.

[Example by Zoning]

FIG. 14 is a block diagram of the data processing system whererestriction is imposed on access by zoning.

The migration control host 112 of the data processing system is providedwith a SAN-controlling API (Application Program Interface) 1401 for thecontrol of the network. The migration control program 113 imposesrestriction on access in the SAN 102 in each phase by using theSAN-controlling API 1401. Because the configuration of this dataprocessing system, except the SAN-controlling API 1401, is the same asthe configuration of the data processing system of FIG. 1, detaileddescription is omitted here.

FIG. 15 is an illustration of restriction of access of the dataprocessing system by zoning.

Zoning means to divide ports of fibre channels into groups (zones) byusing their ID numbers (World Wide Names or WWNs). Which host computer101 is accessing which storage subsystem 103 is identified by usingfibre channel switches configuring the SAN 102, and switches are turnedon and off to prohibit access to another zone or from another zone. Thephase before route change 505, route-changing phase 506, data-migrationphase 507, and phase after data migration 508 of data migration shown inFIG. 5 correspond to FIGS. 15 a, b, c, and d, respectively.

The host computer 100, the old storage subsystem 103 a, and the newstorage subsystem 103 b are connected to the SAN 102.

Formed in the phase before route change 505 is a zone 1501 whichincludes the host computer 101 and the old storage subsystem 103 a andexcludes the new storage subsystem 103 b; accordingly, the host computer101 cannot access the new storage subsystem 103 b (FIG. 15 a).

Formed in the route-changing phase 506 is a zone 1502 which includes thehost computer 101 and the old and new storage subsystems 103 a and 103b; accordingly, the host computer 101 can access both the old and newstorage subsystem 103 a and 103 b, and hence the route change of thehost computer 101 is possible (FIG. 15 b).

When the route change of the host computer 101 is completed, the systemadvances into the data-migration phase 507, wherein access to the oldstorage subsystem 103 a has to be prohibited. Accordingly, formed in thedata-migration phase 507 is a zone 1503 which includes the host computer101 and the new storage subsystem 103 b and excludes the old storagesubsystem 103 a. In addition, a zone 1504 is formed to include the oldand new storage subsystems 103 a and 103 b. The zone 1503 enables thehost computer 101 to access the new storage subsystem 103 b, and thezone 1504 enables the migration of data from the old storage subsystem103 a to the new one 103 b (FIG. 15 c).

In the phase after data migration 508, the zone 1504 is eliminatedbecause access from the new storage subsystem 103 b to the old one 103 ais unnecessary. The zone 1503 alone is left and is continued to be usedfor access from the host computer 101 to the new storage subsystem 103 b(FIG. 15 d).

In the same way, restriction can be imposed on access by using a VLAN inEthernet (a registered trademark).

[Example by Storage Subsystems]

The storage subsystem 103 is usually provided with a function ofrestricting access to its volumes 105 called “LU security” (hereinafter“storage security function”). In the embodiment described below, accesscontrol during data migration processing is accomplished by using thestorage security function.

FIG. 16 is a block diagram of the data processing system wherein accesscontrol is accomplished by the storage security function. The migrationcontrol host 112 of the data processing system is provided with astorage subsystem-controlling API (Application Program Interface) 1601for the control of the network. The migration control program 113imposes restriction on access in the SAN 102 in each phase by using thestorage subsystem-controlling API 1601. For the access restriction,various identifiers can be used such as identifiers logically allottedto the host computers (identifiers used on the networks including the IPaddress), identifiers physically allotted to network interfaces (forexample, the MAC address of Ethernet, the WWN of the fibre channel,etc.), and identifiers logically allotted to network interfaces (forexample, the iSCSI Name). Because the configuration of this dataprocessing system, except the storage subsystem-controlling API 1601, isthe same as the configuration of the data processing system of FIG. 1,detailed description is omitted here.

FIG. 17 is an illustration of restriction of access of the dataprocessing system by the storage security function.

The phase before route change 505, route-changing phase 506,data-migration phase 507, and phase after data migration 508 of datamigration shown in FIG. 5 correspond to FIGS. 17 a, b, c, and d,respectively.

The host computer 101, the old storage subsystem 103 a, and the newstorage subsystem 103 b are connected to the SAN 102.

In the phase before route change 505, the migration-control program 113sets such that the host computer 101 can access the old storagesubsystem 103 a and external devices cannot access the new storagesubsystem 103 b (FIG. 17 a).

In the route-changing phase 506, the migration-control program 113 setssuch that the host computer 101 can access both the old storagesubsystem 103 a and new storage subsystem 103 b. Since the new storagesubsystem 103 b has to access the old storage subsystem 103 during theroute change, the migration-control program 113 sets such that the newstorage subsystem 103 can also access the old storage subsystem 103 a(FIG. 17 b).

When the route change of the host computer 101 is completed, the systemadvances into the data-migration phase 507, wherein access to the oldstorage subsystem 103 a has to be prohibited. Accordingly, in thedata-migration phase 507, the migration control program 113 sets suchthat the host computer 101 cannot access the old storage subsystem 103 aand the new storage subsystem 103 b can access the old storage subsystem103 a. The migration of data is executed by the access of the newstorage subsystem 103 b to the old storage subsystem 103 a. As in theroute-changing phase 506, the new storage subsystem 103 b is made to beaccessible from the host computer 101 (FIG. 17 c).

In the phase after data migration 508, it is no more necessary for thenew storage subsystem 103 b to access the old storage subsystem 103 a;accordingly, the migration-control program 113 prohibits all the accessto the old storage subsystem 103 a. Further, the migration-controlprogram 113 keeps the new storage subsystem 103 b to be accessible fromthe host computer 101 (FIG. 17 d).

[Combination]

Referring to FIGS. 13 through 17, embodiments in which accessrestriction can be accomplished in the network 102 and storage subsystem103 have been described. However, by combining the access restriction onthe side of the network and on the side of the storage subsystem 103,stronger restriction of access can be accomplished.

[Data Migration with a Debugging Mode]

In the route-changing processing, it is necessary to ascertain settingof a new route. Therefore, a debugging mode may be provided in theroute-changing processing (303 of FIG. 3). In this case, route changeswith respect to all the host computers 101 must be executed at the sametime.

FIG. 18 is a flowchart of data-migration processing with a debuggingmode of the data processing system of FIG. 1.

As in the previously described initialization of FIG. 3 (301), in thephase before migration, the migration-control program 113 initializesthe system for data migration (1801).

After the initialization, as in the processing of FIG. 3 (302), the newstorage subsystem 103 b is added to the data processing system (1802).

Then, new routes are provided to all the host computers 101 related tothe data migration (1803). At the same time, the debugging mode of thenew storage subsystem 103 b is turned on.

In the debugging mode, access to the old storage subsystem 103 a isprohibited. The new storage subsystem 103 b stores the data written bythe host computer 101 in itself. With respect to the written data,information of the update data is stored in the bit-map format.

In response to a read request from the host computer 101, the newstorage subsystem 103 b refers to the bit map for update information.When the data are written in the new storage subsystem 103 b, such dataare read from the new storage subsystem 103 b. On the other hand, whenthere is no written data in the new storage subsystem 103 b, data areread from the old storage subsystem 103 a and sent to the host computer101.

Then, the route is checked by executing a test program in the hostcomputer 101 to see if the newly set route is correct or not (1804).

If the route is not correctly set, when the test program tries to accessthe old storage subsystem 103 a while the test program is running, thereoccurs an error because the old storage subsystem 103 a is inaccessible(1805). Then, it is checked whether the number of errors is within theprescribed number or not. (1806). An upper limit to the number of errorsis set in advance. If the number of errors is within the prescribednumber, the setting is revised (1807) and data are restored (1808).Then, the process returns to the step 1803 and the test program isexecuted again.

On the other hand, when the number of errors exceeds the prescribednumber, the new storage subsystem 103 b discards the written data, andexecutes data-restoring processing, which returns the data to a statewhen the new storage subsystem was added (phase before routechange)(1809). The data-restoring processing may be executed by deletingthe data written in the new storage subsystem 103 b. However, it can beaccomplished by deleting all the update information recorded in thebit-map format. Then, the data-migration processing is completed.

Further, when it is ascertained that the test program is normallyfinished and the route is correctly set, the data-restoring processingis executed in which the data are returned to the state before the routechange (1810). Then, the data-migration processing is executed (1811).In the data-migration processing (1811), the same processing as in thedata-migration processing (304) of FIG. 3 is executed.

During the migration processing (the steps 1803 through 1811), the newstorage subsystem 103 b can access the old storage subsystem 103 a andthe host computer 101 can access the new storage subsystem 103 b.

FIG. 19 shows workings of the old storage subsystem 103 a and the newstorage subsystem 103 b in each phase of the data-migration processingwith a debugging mode (FIG. 18).

In the debugging phase (1906), the host computer 101 can't access theold storage subsystem 103 a. With respect to reading from the newstorage subsystem 103 b, non-updated data are read from the old storagesubsystem 103 a and updated data are read from the new storage subsystem103 b to be sent to the host computer 101, which conducts reading. Withrespect to data-writing processing by the host computer 101, all thedata are stored in the new storage subsystem 103 b.

Further, since each of the phase before route change, data-migrationphase and phase after data migration is the same as the one in FIG. 5,the description for it is omitted.

As described above, according to the embodiments of the presentinvention, the route-changing phase is provided before the datamigration, and access from the host computer is made possible evenduring the route-changing phase, which enhances the system availabilityduring the data migration.

To put it concretely, data migration is executed for every volume, theroute-changing phase is provided, and routes of host computers relatedto the volumes whose routes are being changed are sequentially switched.While a plurality of host computers are accessing the volumes whoseroute changes are in progress, the host computer before the route changeaccesses the old storage subsystem, and the host computer after theroute change accesses the new storage subsystem. To ensure theconsistency of data in the old storage subsystem and the new storagesubsystem, all the update information is to be reflected in the oldstorage subsystem. The host computer before the route change writes andreads data to and from the old storage subsystem. Further, with respectto the access from the host computer after the route change to the newstorage subsystem, during the data-reading processing, the data read bythe new storage subsystem from the old storage subsystem are sent to thehost computer. During the data-writing processing, data are written intothe new storage subsystem.

In this way, even during the route-changing phase, it is made possiblefor both the access from the route-unchanged host computer to the oldstorage subsystem and from the route-changed host computer to the newstorage subsystem to be achieved at the same time. Further, in theroute-changing phase, the latest data are stored in the old storagesubsystem and the consistency of data between the old storage subsystemand the new storage subsystem is ensured, enhancing the availability ofthe system in the data-migration processing.

The function according to the present invention can also be accomplishedby the new storage subsystem alone, and there is no need to add newfunctions to the old storage subsystem.

1. A method of migrating data from an old storage subsystem to a newstorage subsystem in a data processing system which includes a pluralityof host computers and a plurality of storage subsystems said methodcomprising the steps of: conducting a route-changing phase beforemigration of the data from the old storage subsystem to the new storagesubsystem; in said route-changing phase, sequentially changing anindication of access destination storage subsystems in said hostcomputers such that an indication of the access destination storagesubsystem of a first host computer is changed from said old storagesubsystem to said new storage subsystem, an indication of the accessdestination storage subsystem of a second host computer is unchangedfrom said old storage subsystem to said new storage subsystem, and thenan indication of the access destination storage subsystem of the secondhost computer is changed from said old storage subsystem to said newstorage subsystem after the access destination storage subsystem of thefirst host computer has been changed, thereby permitting each hostcomputer to access both the old and new storage subsystems; and in saidroute changing phase, by said new storage subsystem, reading data fromsaid old storage subsystem in response to a read request from a saidfirst host computer, sending the data to said first host computer, andwriting data into said old storage subsystem in response to a writerequest from said first host computer.
 2. A method of migrating dataaccording to claim 1, further comprising the step of: by said newstorage subsystem, writing data into said old storage subsystem inresponse to a write request from said host computer in saidroute-changing phase and informing said host computer of completion ofsaid writing after ascertaining data writing processing has beencompleted.
 3. A method of migrating data according to claim 1, whereinsaid new storage subsystem writing data into said old storage subsystemin response to a write request from said host computer and informingsaid host computer write processing has been completed.
 4. The method ofmigrating data according to claim 1, wherein a phase is provided beforesaid route-changing phase in which a route is set such that access fromsaid host computer to said new storage subsystem is prohibited andaccess from said host computer to said old storage subsystem is allowed.5. A method of migrating data according to claim 1, wherein adata-migration phase is provided after said route-changing phase inwhich a route is set such that access from said host computer to saidold storage subsystem is prohibited and access to said new storagesubsystem is allowed.
 6. A method of migrating data according to claim1, wherein, in a data-migration phase, said new storage subsystem readsdata from said new storage subsystem and sends the data to said hostcomputer when the read request from said host computer is directed to adata-migration area, and wherein said new storage subsystem reads datafrom said old storage subsystem and sends the data to said host computerwhen the read request from said host computer is directed to adata-unmigrated area.
 7. A method of migrating data according to claim1, wherein a route is set such that access from said host computer tosaid old storage subsystem is prohibited and access to said new storagesubsystem is allowed even after completion of a data-migration phase. 8.A method of migrating data according to claim 1, wherein an access routeto said new storage subsystem is set by at least one of a plurality ofmethod of changing a form of connection among said host computer, saidold storage subsystem and said new storage subsystem, wherein saidmethod further comprises: using access restriction by a networkconnecting said host computer, said old storage subsystem and said newstorage subsystem, and using access restriction by said storagesubsystem.
 9. A method of migrating data according to claim 1, wherein aroute verification process is performed by which a route set in saidroute-changing phase is determined to be correct or not before migratingthe data from said old storage subsystem to said new storage subsystem.10. A method of migrating data according to claim 9, wherein a route isset such that access from said host computer to said old storagesubsystem is prohibited and access to said new storage subsystem isallowed during said route verification process, wherein said new storagesubsystem writes data requested by said host computer to said newstorage subsystem and stores written data, wherein said new storagesubsystem, in response to a read request from said host computer, refersto said written data and checks to see if the data stored in said newstorage subsystem during said route verification process are updated,wherein when the data stored in said new storage subsystem are updatedduring said route verification process, the data are read from said newstorage subsystem and sent to said host computer, and wherein, when thedata stored in said new storage subsystem are not updated during saidroute verification, the data are read from said old storage subsystemand sent to said host computer.
 11. A method of migrating data accordingto claim 9, wherein data updated during said route verification processare discarded when the set route is determined to be incorrect and astate is returned to a state before route change.
 12. A method ofmigrating data according to claim 9, wherein data updated during saidroute verification process are discarded when the set route isdetermined to be correct, and data-migration processing is executedafter returning to a state before route change.
 13. A method ofmigrating data from an old storage subsystem to a new storage subsystemin a data processing system which includes a plurality of host computersand a plurality of storage subsystems connected to said plurality ofhost computers, said method comprising the steps of: conducting aroute-changing phase before migration of the data from the old storagesubsystem to the new storage subsystem; in said route-changing phase,sequentially changing an indication of access destination storagesubsystems in said host computers such that an indication of the accessdestination storage subsystem of a first host computer is changed fromsaid old storage subsystem to said new storage subsystem, an indicationof the access destination storage subsystem of a second host computer isunchanged from said old storage subsystem to said new storage subsystem,and then an indication of the access destination storage subsystem ofthe second host computer is changed from said old storage subsystem tosaid new storage subsystem after the access destination storagesubsystem of the first host computer has been changed, therebypermitting said host computers to include route-changed host computersaccessing said new storage subsystem and route-unchanged host computersaccessing said old storage subsystem, in said route changing phase, bysaid new storage subsystem, reading data from said old storage subsystemin response to a read request from a route-changed host computer andsending the data to said route-changed host computer, in said routechanging phase, by said new storage subsystem, writing data into saidold storage subsystem in response to a write request from saidroute-changed host computer and informing said route changed hostcomputer of completion of processing after ascertaining completion ofdata-writing processing, in said route changing phase, by said oldstorage subsystem, reading data and sending the data to a route changedhost computer in response to a read request from said route-unchangedhost computer, and in said route changing phase, by said old storagesubsystem, writing data in response to a write request from saidroute-unchanged host computer and informing said route-changed hostcomputer of completion of processing after ascertaining completion ofdata-writing processing.